Artificial Light at Night (ALAN), an alarm to ovarian physiology: A study of possible chronodisruption on zebrafish (Danio rerio)

Jul 27, 2018The Science of the total environment

Artificial Light at Night May Disrupt Ovarian Function in Zebrafish

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Abstract

A total of 1791 genes were significantly upregulated in ovarian tumors induced by artificial light at night (ALAN) in zebrafish.

Continuous exposure to light led to desynchronization of clock-related genes in zebrafish, affecting their reproductive biology.
Loss of rhythmicity and lower melatonin levels were observed in the brain, retina, ovary, and serum under varying light conditions.
Increased expression of NF-κB and inflammatory cytokines was noted, suggesting a link to tumorigenesis.
Histological analysis confirmed the formation of thecoma and granulosa cell tumors after one year of light exposure.
RNA sequencing indicated the upregulation of genes associated with other physiological disorders linked to tumor development.

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The ALAN is drawing the attention of researchers and environmentalists for its ever-increasing evidence on its capacity of "desynchronization" of organismal physiology. Photoperiod and circadian cycles are critical parameters to influence the biology of reproduction in several animals, including fish. The present study is the first proof of the development of an ovarian tumour with the effect of light in zebrafish (Danio rerio), an excellent model for circadian-related studies. Results of three experimental conditions, continuous light for one week, LLW, one month, LLM, and for one year, LLY revealed a clear desynchronization of clock associated genes (Clock1a, Bmal1a, Per2, and Cry2a). Interestingly, loss of rhythmicity and low concentration of melatonin found in these conditions in whole brain, retina, ovary, and serum through ELISA. RNA-Seq data of ovarian samples revealed the upregulation of Mid2, Tfg, Irak1, Pim2, Tradd, Tmem101, Nfkbib genes and ultimately increase the expression of NF-κB, a cellular transformer for tumourigenesis, confirmed by the western blot. The appearance of TNFα, inflammatory cytokines and activator of NF-κB also increased. Histology approved the formation of thecoma and granulosa cell tumour in the one year exposed ovarian sample. The whole transcriptome data analysis revealed 1791 significantly upregulated genes in an ovarian tumour. Among these genes, DAVID functional annotation tool identified 438 genes, directly linked to other physiological disorders. This study evidenced of an ovarian tumour induced by ALAN in zebrafish.

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Artificial Light at Night (ALAN), an alarm to ovarian physiology: A study of possible chronodisruption on zebrafish (Danio rerio)

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